Optimized drilling methods lead to increased success rate and reductions in rig time
The drilling of Eagle Ford horizontal wells in Karnes and DeWitt counties traditionally requires at least two bottomhole assembly (BHA) configurations to drill from surface casing to reach total depth (TD). After a few initial successful attempts at drilling from surface casing to TD using a single BHA (one-run), several problems were encountered, resulting in multiple unsuccessful one-run attempts. What began as a study to determine the best bit for one-run applications evolved into a multivariable study to identify the key factors for achieving successful one-run wells.
The success rate of one-run wells increased from 25 to 85% over a seven-month period. Achieving this level of success involved analyzing vertical parameters (specifically through the highly abrasive Wilcox formation), geographic location (correlated with Wilcox formation thickness), motor bend, BHA components, well trajectory, bit selection, and overall well length. Improving the efficiency of drilling Eagle Ford wells with a one-run application proved to be most dependent on the optimization of vertical parameters, Wilcox thickness, and overall well length.
The method and recommendations presented in this paper are most applicable on land. Wells with geologic formations and temperature ranges that can tolerate necessary variations in mud parameters throughout the vertical, curve, and lateral sections should be seriously considered. One-run wells can prove profitable by sacrificing a section rate of penetration (ROP) to gain overall well ROP. For example, a slight reduction of the drilling parameters in the vertical section may reduce the vertical ROP, but will maintain the BHA integrity for the curve and lateral sections, which will result in an increased ROP for the length of the well.
Significant reductions in rig time and the amount of equipment used resulted in an overall increased economic efficiency dependent on time and costs associated with tripping and picking up a new BHA. In addition, eliminating a trip for a new BHA is a simpler operation and, consequently, provides a safer work environment for rig personnel.
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Source: Unconventional Resources Technology Conference, 20-22 July, San Antonio, Texas, USA
Authors: Kathryn J. Patton (Halliburton) | Luke S. Walker (BHP Billiton)